Ore-Grade Nickel Hosted in Fine-Grained Sedimentary Rocks, Jezero Crater, Mars

Introduction: In 2024, the Perseverance rover explored Neretva Vallis, an inlet valley which once brought water into Jezero Crater, Mars. In Neretva Vallis, the rover encountered variably oxidized mudstones transected by erosion-resistant veins and fractures. These sedimentary rocks were investigated using SuperCam [1,2] – a mast-mounted spectroscopy instrument capable of Laser Induced Breakdown Spectroscopy (LIBS), visible-near infrared and Raman spectroscopy. LIBS works by focusing a laser onto a target at a distance of up to several meters and generating a small plasma. As the plasma decays, light is emitted at wavelengths specific to the elements present in the sample, allowing geochemical analysis of the targets. In Neretva Vallis, SuperCam detected significant enrichments in nickel (Ni), including the highest concentration ever observed in Martian bedrock (~1.2 wt.%). In this work, SuperCam and PIXL (micro-XRF) data are used to contextualize this discovery and explore its implications for the emplacement and alteration history of Neretva Vallis.

Results: Ni detections with SuperCam are highly localized within the northern and southernmost portions of Neretva Vallis. In the north, this is within the “Beaver Falls” workspace, where the rover examined the contact between the dominant mudstones of Neretva Vallis and the adjacent olivine/Fe-carbonate-rich margin unit. SuperCam detected significant Ni enrichments on both sides of this contact, with particularly strong concentrations (up to ~0.63 wt.%) in an olivine-rich conglomerate interpreted as a debris flow sourced from the Margin Unit [3]. In the south, Perseverance took measurements in the highly oxidized mudstones of the “Wallace Butte” workspace. Here SuperCam found substantial Ni enrichments in the bulk mudstone, including the “Dragon Creek” target, which averaged ~1.1 wt.% Ni over ten individual LIBS observations. A correlation between Fe and Ni was observed, indicating that Ni is likely hosted in a Fe-rich phase. The Fe:Ni ratio was ~60-90 for most targets.

PIXL, an arm-mounted X-ray fluorescence (XRF) instrument that produces mm- to cm-scale elemental maps [4], found Ni concentrated within ~1–1.5 mm zones of Fe-sulfide and Mg/Ca-sulfate, consistent with rounded grains or nodules, as well as linear ~0.3 wide sulfide/sulfate veins. Limited counting statistics, diffraction, and the Fe K_β tailing currently limit direct comparison of absolute abundances of Ni between PIXL and SuperCam.

 Discussion: The presence of Ni-rich, anhedral, and dispersed ~1–1.5 mm Fe-sulfide nodules, as well as linear veins, within a mudstone is reminiscent of authigenic pyrite in sedimentary rocks from Earth’s early history. The Ni content of ancient pyrite nodules has been used on Earth to track changing ocean conditions and interactions with igneous events, including the emplacement of large igneous provinces [5,6]. The provenance of Ni in Neretva Vallis is difficult to determine without isotopic or co-occurring trace element data but the Mg-poor composition of Bright Angel mudstones argues against local sourcing from the adjacent ultramafic margin unit.

Ni impurities in greigite (Fe₃S₄), a precursor to authigenic sedimentary pyrite on Earth, resemble proteins that are essential to early microbial carbon fixation and have therefore been proposed as key to abiogenesis [7]. The detection of major Ni enrichments in fine-grained sedimentary rocks, spatially related to zones of locally reduced sulfur (‘leopard spots’) and the first detection of G-band organics with SHERLOC Raman spectroscopy [8], could provide another hint at potential organic processes.

 References: [1] Wiens R. C. et al. (2021) Space Sci Rev, 4, 217. [2] Maurice S. et al. (2021) Space Sci Rev, 47, 217. [3] Jones et al. (2025) Lunar and Planetary Science Conference. [4] Allwood A. C. et al. (2020) Space Sci Rev, 134, 216. [5] Large R. R. et al. (2014) Earth Planet. Sci. Lett., 209-220, 389. [6] Gregory D. et al. (2019) Geoch. Cosm. Acta¸ 53-68, 259. [7] Russell M. J. and Martin W. (2004) Trends in Biochem. Sci., 358-363, 29. [8] Hurowitz et al. (2025) Lunar and Planetary Science Conference.